So if you're working with cyanide in the lab as potassium cyanide or sodium cyanide, those are what are called p h s's, it's a rating for different kinds of chemicals.

因此如果你在实验室中,需要用到氰化物，比如氰化钾或者氰化钠，这就是所谓的，“P，H，S“,这是化学药品有害程度的一个级别。

麻省理工公开课 - 化学原理课程节选